1. Field of the Invention
The invention relates generally to cooling systems. More specifically, the invention relates to a system and method for cooling a nitrogen enriched air stream as it passes through an air separation module (ASM) of an On-board Inert Gas Generating Systems (OBIGGS).
2. Description of Related Art
The energy requirements of most modern aircraft are supplied by combusting aviation gasoline, which is typically stored in fuel tanks within an aircraft's wings. Such fuel tanks also contain an explosive fuel/air mixture in the area above the fuel, otherwise known as the ullage. Accordingly, many systems have been developed to reduce the danger of accidentally igniting this air/fuel mixture.
One way of addressing such a danger is to replace the explosive air/fuel mixture with a nonflammable inert gas, usually nitrogen. The On-board Inert Gas Generating System (OBIGGS) does just this, by separating nitrogen from local, ambient air and replacing the fuel/air mixture in the ullage with this nitrogen.
Military aircraft have used OBIGGS systems for many years to protect against fuel tank explosions caused by extreme aircraft operation and exposure to small arms fire. However, military aircraft are not the only aircraft that would benefit from OBIGGS. For example, investigations into the cause of recent air disasters have concluded that unknown sources may be responsible for fuel tank ignition and explosion. Subsequently, OBIGGS has been evaluated as a way to protect commercial aircraft against such fuel tank explosions caused by any ignition source.
Prior OBIGGS systems have proved relatively unreliable, heavy, and costly for both initial acquisition and non-military operation. Accordingly, a need exists for a reliable, simple, light, and inexpensive OBIGGS system for commercial aircraft application.
Moreover, the inert gas introduced into the ullage must be at a relatively low temperature. To ensure that the inert gas is at a sufficiently cool temperature, current OBIGGS systems typically pre-cool the air entering the ASM of the OBIGGS system using bulky and expensive heat exchangers. Such a heat exchanger is shown in U.S. Pat. No. 4,556,180. Accordingly, a system and method for cooling the inert air before it is introduced into the ullage, while eliminating the use of bulky and costly heat exchangers, would be highly desirable.